Centrifuges



Nov. 7, 1961 A. BOYLAND 3,007,629

CENTRIFUGES Filed Feb. 19. 1947 2 Sheets-Sheet 1 l7 DRIVING MOTOR ANDVACUUM GLAND I5 20 I9 I 8 EVACUATING PUMP IN VEN TOR.

EVACUATING PUMP United States Patent 3,007,629 CENTRIFUGES Donald ArthurBoyland, Kenton, Middlesex, England ljlle d Feb. 19, 1947, Ser. No.729,600 Claims priority, application Great Britain Feb. 27, 1946 Claims.(Cl. 233-21) This invention relates to centrifuges comprising rotorsarranged for operation at high peripheral velocities and has for oneobject the provision of improved means of w thdrawing from the rotor thelighter fractions of centrifuged fluid.

In centrifuges operating at high speeds, for example for the separationof gases of high molecular weight, the pressure difference inside therotor between the axial region and the peripheral region is substantial.Whereas in an evaporative centrifuge the pressure at the periphery maybe of the order of 1000 mm. Hg, the pressure near the axis, where theconcentration of the lighter constituent of the fluid is greatest, maybe of the order of 0.001 millimetre of mercury or less. Difliculty thenarises in the withdrawal of the fluid from the axis of the rotor at arate adequate to maintain useful separation of the constituents.

A further object of the invention is to enable the exhaust aperturesthrough which fluid is withdrawn from the rotor of a centrifuge to bemade of generous area without undue mechanical weakening of the rotorstructure.

Other objects of the invention will be apparent from the followingdescription and from the appended claims. In accordance with the presentinvention there are provided in the rotor radial channels or sectionscommunieating with the axial part of the main space within the rotor andwith an external exhaustchamber so that the light fraction of the fluidis evacuated by a centrifugal pumping action within the centrifuge inconjunction with such normal external pumping as may be necessary.

The adoption of this form of construction, in which part of the pumpingmeans for exhausting the centrifuge is made integral with the centrifugerotor, enables the exhaust apertures in the centrifuge proper to be madeof generousarea without undue mechanical weakening of the rotorstructure. This eliminates difficulties which arise when attempts aremade to exhaust gas at low pressure through small-area outlets from acentrifuge.

The invention will be described by Way of example with reference to theaccompanying drawings in which FIG. 1 is a somewhat diagrammaticpart-sectional View one the line I-I of FIG. 2 of a centrifuge accordingto the invention,

FIG. 2 is a view in cross-section to an enlarged scale of the rotor ofthe centrifuge of FIG. 1, and

FIG. 3 is a fragment of the view in FIG. 2 and illustrates amodification according to the invention.

Referring to FIGURES 1 and 2, a centrifuge comprises a fixed outercasing consisting of a cylindrical body and two end plates 11 and 12.Within the casing is rotatably mounted a rotor, of length substantiallygreater than its diameter, comprising a substantially cylindrical shell13, having the contour shown in FIGURE 2 which forms the subject ofBritish patent specification No. 6,125/46, having its ends closed by endplates 14 and 15. The rotor is suspended by a hollow spindle 16 whichpasses through suitable glands (not shown) to a driving motor 17 whichmay for example be of the turbine type. At the lower end of the rotor isa hood 18 having an upturned flange 19 overlapping a spigot 20' on theend plate and forming therewith a labyrinth packing to prevent excessivepassage of gaseous fluid. Within the flange 19 is a boss 21 connected tothe flange by spider arms 22. p The boss is apertured to receive a shortspindle 23 projecting from the endplate 15 to provide a lower bearingfor the rotor, the bearing being connected by the spider arms 22 to thehood 18.

The hood 18 is slidably mounted on a seating 24 carried by a partition24 apertured at 25. The slidable mounting permits of small amounts ofmotion of the lower end of the rotor (for example when passing through acritical speed), and the friction between the surfaces of hood 18 andseating 24 provides desirable damping. An exhaust pipe 26 is fixed tothe partition in communication with the space 27 within the hood 18 andextends through the end plate 12 to the outside and thence to a pump 28.The space within the casing 10, 11, 12 and without the rotors 13, 14, 15is in connection through aperture 25 with a pipe 29 through which thisspace may be evacuated by means of a pump 30.

The rotor comprises radial webs 31 and sheet metal partitions 32 bothextending over substantially the whole internal axial length of therotor. The partitions 32 are anchored along their inner edges 33 to thehub portion 34 of the rotor at the roots of the webs 31 and'are fixed tothe webs 31 at an intermediate radial distance along them as at 35.Apertures 36 connect the interior of the extraction chambers formedbetween the webs 31 and the partitions 32 with the space 27, theseapertures being near the radially outer parts of the extractionchambers. The partitions are apertured at 37 near the radially innerparts of the extraction chambers to connect these chambers with thespace within the rotor and without the extraction chambers.

In operation fluid to be centrifuged is introduced into the rotorthrough the hollow spindle 16 and passages 38.

I When the rotor is rotated at high speed, the lighter fractioncollecting near the axis passes through the apertures 37 into theextraction chambers enclosed by partitions 32 and webs 31, iscentrifuged outwards to emerge through apertures 36 into the space 27within the hood 18 and from here is pumped out through the pipe 26 bythe pump 28. A suitable vacuum is maintained in the space be tween therotor and the casing by the pump 30 which also extracts any of thelighter fraction which reaches this space. 1

The fact that the only inlets 37 to the extraction chambers are near theaxis of the rotor ensures that only the lighter fraction enters thesechambers whilst the disposition of the outlets 36 from these chambers ata substantially greater radial distance from the axis than the inlets,provides a substantial increase in the pressure of the lighter fractionat the outlets compared with the inlets. The chambers, therefore,materially assist the extraction or removal of the lighter fraction fromthe interior of the rotor.

The provision of apertures 37 distributed along the axial length of therotor has the advantage that fluid can pass into the extraction chambers32 from the space within the rotor and without the extraction chambersin a radial direction without any appreciable axial component ofmovement. which tends to occur when there is any considerable axialcomponent of flow of the fluid. A further advantage of the use of anumber of apertures is that their total crosssectional area can be maderelatively large in the region where the pressure is low. Thecross-sectional area of the passages 36 can on the other hand berelatively small since they are situated where the pressure isrelatively high, namely in the radially outer regions of the extractionchamber.

During the separation process, the fraction that is at any time beingremoved from the rotor, will be lighter This prevents re-mixing ofconstituentsing of the last fraction into the last container may becontinued until the rotor has been substantially emptied of fluid.Alternatively, the centrifuging process may be interrupted at any timeby allowing the rotor to come to rest, the residue within the rotorbeing then removed in any convenient manner.

During operation of the centrifuge a substantial pressure gradientobtains in a radial direction in the extraction chambers as in the maincavities of the rotor. Hence a usefully high pressure of exhaust gas ismaintained and the pump 28 is therefore substantially assisted by thecentrifugal pumping effect within the extraction chambers.

The gas which emerges from the rotor may be allowed to flow directlyinto the space between the rotor and the stationary casing instead ofinto the hood 18. It will, however, be appreciated that, with a veryhigh speed rotor, it is desirable (as a practical matter) to run it in aspace maintained at a comparatively low pressure in order to preventexcessive windage losses. Where the gas is allowed to discharge directinto the casing, it then becomes necessary to provide pumps which willmaintain a sufficiently low pressure in the casing despite the eflluentgas from the rotor. Where the gas emerges in a separate end hood asshown in FIGURE 1, the capacity of the pump 30 used for exhausting themain casing can be somewhat reduced since the pump has to deal only withthat part of the eflluent gas from the rotor which succeeds in leakingthrough the narrow clearance between 19 and 20.

In an evaporative centrifuge, fluid vapourising near the periphery andmoving inwardly suffers a continuous fall-in circular speed. Hence itspressure on the forward web is greater than on the rear web.Accordingly, when the direction of rotation is that indicated by thearrow 39 in FIGURE 2, it is preferable to locate each partition 32 asshown adjacent to the forward web of each compartment of the rotor totake advantage of the higher pressure existing there.

The partitions 32 may be relatively rigid but they are preferablyflexible so that during rotation of the rotor they are suspended asloops between their anchorages 33 and 35. If they are made relativelyrigid, their shape may approximate to such suspended loops.

Another construction of the extraction chambers is shown in FIGURE 3.Here they are constituted by a flexible metal sheet 40, for example of asuitable aluminum alloy, extending substantially the full internal axiallength of the rotor and formed as complete loops. The material of theloops may be quite thin. The two walls of the loops are apertured at 41.The inner end of the loop is anchored to the hub of the rotor by a solidkey or wedge 42 and the outer end may be located by bosses such as 43upon the end plates of which only the plate is shown. Apertures 36' areprovided, as in FIGURES 1 and 2, to connect the extraction chambersenclosed by the loops with the space 27 of FIGURE 1.

Where gases at very low pressures are to be pumped away from the centralregion near the hub 34, the circumferential cross section of the loop inthis central region should have an area of approximately the same valueas the cross sectional area remaining in the segment external to theloop. Thus, referring to FIGURE 3, the circumferential length betweenpoints A and A along a circle passing through the centres of apertures41 should be approximately equal to half the circumferential lengthalong the same circle between points B and B.

The material forming the outside edge 44 of the loops should be stiffenough to withstand the slight bending forces necessary to keep the twowalls of the loop at the correct distance apart.

I claim:

1. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, an external exhaustchamber within said casing but exterior to said rotor for receiving arelatively light fraction of said fluid, at least one extraction chamberwithin said rotor extending over at least the greater part of the axiallength of said rotor and apertured at at least a plurality of pointsdistributed along its axial length relatively near said axis to receivesaid lighter fraction from the space within said rotor and without saidextraction chamber, and a fluid passage for said lighter fractionconnecting a region of said extraction chamber relatively remote fromsaid axis with said exhaust chamber.

2. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, an external exhaustchamber within said casing but exterior to said rotor for receiving arelatively light fraction of said fluid, a plurality of extractionchambers within said rotor and extending radially with respect to saidaxis extending over at least the greater part of the axial length ofsaid rotor and having walls apertured at at least a plurality of pointsdistributed along their axial length in a region relatively near to saidaxis to communicate with the space within said rotor and without saidextraction chambers and apertured in a region relatively remote fromsaid axis to communicate with said exhaust chamber.

3. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, an external exhaustchamber within said casing but exterior to said rotor for receiving arelatively light fraction of said fluid, pump means for withdrawing saidlight fraction from said rotor to said exhaust chamber and centrifugalmeans within said rotor for assisting said withdrawal, said centrifugalmeans comprising at least one chamber extending radially with respect tosaid axis, extending over at least the greater part of the axial lengthof said rotor and having a wall apertured at at least a plurality ofpoints distributed along its axial length and in a region relativelynear said axis to communicate with the space within said rotor andWithout said extraction chamber and apertured in a region relativelyremote from said axis to communicate with said exhaust chamber.

4. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis and provided with an inlet passage for theintroduction into said rotor of fluid to be centrifuged therein, saidrotor comprising a substantially cylindrical shell, end plates formingclosures at each end of said shell, a hub portion and a plurality ofwebs extending between said end plates and connecting said shell andsaid hub portion, and a partition associated with at least one of saidWebs, extending between said end plates and forming with a part thereofand with parts of said end plates the wall of an extraction chamber,said wall being apertured at at least a plurality of points distributedalong its axial length and relatively near to said axis to communicatewith the space within said rotor and without said extraction chamber andapertured relatively remote from said axis for the withdrawal of fluidfrom said rotor.

5. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis and provided with an inlet passage for theintroduction into said rotor of fluid to be centrifuged therein, saidrotor comprising a substantially cylindrical shell, end plates formingclosures at each end of said shell, a hub portion, a plurality of websconnecting said shell and said hub portion, and a partition associatedwith each of said webs, said partition extending between said endplates, having an inner edge connected to said hub portion, an outeredge connected to the associated web and a part intermediate said edgesspaced from the associated web to form an extraction chamber, saidpartitions being apertured at at least a plurality of points distributedalong its axial length and near to said inner edges thereof to providecommunication between the space within each extraction chamber and thespace outside such extraction chamber but within said rotor and at leastone of said end plates being apertured to provide for each of saidextraction chambers near to the radially outer part thereof acommunicating passage between such extraction chamber and the spacewithin said casing but without said rotor.

6. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, pump means forextracting fluid from the space between said rotor and said casing, aplurality of extraction chambers Within said rotor and extendingradially with respect to said axis, extending over at least the greaterpart of the axial length of said rotor and having walls apertured at atleast a plurality of points distributed along its axial length and in aregion relatively near to said axis to communicate with the interior ofsaid rotor outside said chambers and apertured in a region relativelyremote from said axis to communicate with said space.

7. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, a hood fixed to saidcasing and forming with a part of said rotor an exhaust chamber, aplurality of extraction chambers within said rotor and extendingradially with respect to said axis, extending over at least the greaterpart of the axial length of said rotor and having walls apertured at atleast a plurality of points distributed along its axial length and in aregion relatively near to said axis to communicate with the space withinsaid rotor and without said extraction chamber and apertured in a regionrelatively remote from said axis to communicate with said exhaustchamber.

8. A centrifuge according to claim 2, wherein each of said extractionchambers within said rotor is constituted by a closed loop of flexiblemetal sheet having its inner end anchored to the rotor near the axisthereof.

9. A centrifuge for centrifuging fluid comprising a casing which inoperation is fixed, a hollow rotor mounted for rotation within saidcasing about an axis, an inlet passage in said rotor for theintroduction of fluid to be centrifuged therein, an external exhaustchamber within said casing but exterior to said rotor for receiving arelatively light fraction of said fluid, at least one extraction chamberwithin said rotor apertured relatively near said axis to receive saidlighter fraction from the space within said rotor and without saidextraction chamber, and a fluid passage for said lighter fractionconnecting a region of said extraction chamber relatively remote fromsaid axis with said exhaust chamber, said apertures relatively near saidaxis and having a cross-sectional area which is much greater than thatof said fluid passage which is relatively remote from said axis.

References Cited in the file of this patent UNITED STATES PATENTS576,357 Anderson Feb. 2, 1897 621,619 Salenius Mar. 21, 1899 625,067Schroeter May 16, 1899 717,385 Gathmann Dec. 30, 1902 1,208,960Hedderich Dec. 19, 1916 1,695,990- Altpeter Dec. 18, 1928 1,821,6Q7Andersson et a1. Sept. 1, 1931 2,422,882 Bramley June 24, 1947 FOREIGNPATENTS 640,550 Germany Jan. 7, 1937

